1. Field of the Invention
This invention relates to a primer composition. More particularly, it relates to a primer composition suited for the achievement of strong adhesion of silicone rubber on the surface of a metal, plastics or the like.
2. Description of Prior art
Silicone rubber is used for various purposes because of its excellent physical and chemical properties. It is also used as a material to form a composite with metals or plastics. In the manufacture of such a composite, for example, a method is employed in which a primer composition comprising i) an alkoxysilane having an unsaturated bond, such as vinyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane or 3-methacryloxypropyltrimethoxysilane, or a hydrolysis condensate thereof or a co-hydrolysis siloxane, ii) a titanate and iii) a metal salt of an organic fatty acid is previously coated on the surface of a metal or plastics, and thereafter a silicone rubber is applied to the resulting coating, and cured, whereupon the silicon rubber is adhered. The adhesion surface thus formed has the disadvantage that it can not maintain the adhesion for a long period time at temperatures higher than 200.degree. C., for instance, and may cause peeling in high-temperature oils.
In those circumstances, a rubbery composition comprising a vinyl group-containing organopolysiloxane, a polysiloxane resin, an alkoxysilane, an organic peroxide and a catalyst has been proposed as a composition improved in high-temperature resistance and high temperature oil resistance (see Japanese Patent Publication (KOKOKU) No. 30817/1981). This composition can improve the adhesion under conditions of high temperatures and in high-temperature oils, but has the disadvantages not only that it is compositionally so complicated that its manufacture is laborious and time-consuming, but also that part or the whole of a primer layer is peeled because of the flow of the rubber compound injected at the time of injection molding. From the viewpoint of working or processing, the composition also has the disadvantage that it has so poor air-drying properties that constant heating is required to prevent the primer layer from flowing.
Japanese Patent Publication No. 163968/1985 also proposes a primer composition comprising as a main component a silazane bond-containing organosilicone, which has good air-drying properties and high coating strength. This can attain good adhesion, but, from the viewpoint of processing, has the disadvantage that it has a short pot life.